<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
</head>

<body>

    <div id="app">app</div>
    <div class="aaa">aaa</div>
    <button>哈哈</button>
    <button>哈哈</button>
    <button>哈哈</button>
    <button>哈哈</button>
    <button>哈哈</button>

    <ul id="list1">
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>

    <ul id="list2">
        <li>1</li>
        <li>2</li>
        <li>3</li>
    </ul>

    <script src="https://cdn.bootcdn.net/ajax/libs/jquery/3.6.0/jquery.min.js"></script>
    <script>
        $('#app');
        $('.aaa');
        $('button');

        $('#list1 li').on('click', function() {
            console.log(this);
        });
    </script>
</body>

</html>